The present invention relates to a diaphragm pressure switch for controlling small pressure gradients.
It is known that there are at present many types of diaphragm pressure switches having different structures which are intended to detect and, or to indicate and, or to automatically counterbalance pressure gradients or rates of rise or fall which may arise in different circuits or apparatuses.
The common element of these pressure switches is a diaphragm separating two adjacent chambers each of them being in communication with a specific area of the apparatus or circuit to be controlled. The diaphragm is subject to deformation in a manner substantially proportional to the rate of rise or fall of pressure which may occur between the two chambers mentioned above and by its deformations it actuates suitable detecting and, or controlling members. Typically, the diaphragm draws along one or more electrically conductive elements and by said deformation arranges the same so that some electrical contacts are connected to one another. These are connected, for example, to warning lights or to stop members for the devices which may have cause said variation in pressure.
The most important technical drawback of these pressure switches resides in that they are not in a position to detect very small pressure gradients such as for example of a few millibars if they have a small size and a comparatively simple structure. Furthermore, when the diaphragm pressure switches of the kind mentioned above have to detect very small pressure gradients, they appear very irregular and are not sure in operation, which considerably reduces their reliability particularly as to the possibility of constant detections during a long lapse of time. That is a technical disadvantage from a general point of view as it reduces the possibility of applying pressure switches of the kind mentioned above to all usual apparatuses, home apparatuses included, for which said pressure switches woulld be particularly useful.
For example, it would be possible to control the degree of operation of a vacuum cleaner due to the clogging of the filter-bag, or the operation of a hood, or still to control the level of various tanks by using small diaphragm pressure switches simply connected to warning lights suitable to inform any utilizer of an irregularity in operation.
Practical tests have proved that known pressure switches are not suitable for working environments where polluting factors such as dust, hydrocarbon vapors and the like exist, which may hinder the passage of current close to the electrical contacts. It is the same when they are introduced into a working fluid, such as for example some kinds of oils, which has a partial insulating power.